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Abstract:

An exhaust purification system of an internal combustion engine, having
an exhaust purification catalyst in the exhaust passage of the engine of
a vehicle, a fuel supply device provided in the exhaust passage upstream
the exhaust purification catalyst and supplies fuel to an exhaust gas
flowing into the catalyst, a heating device which heats the fuel supplied
from the fuel supply device, and a controller which controls the heating
device. The controller controls the heating device, when a first
processing request based on a state of the exhaust purification catalyst
is standing and a second processing request based on an operating state
of the vehicle is not standing (t2), to a pre-heating temperature lower
than an ignition threshold capable of igniting the fuel and, when the
first processing request and the second processing request are standing
(t3), to an ignition temperature higher than the ignition threshold.

Claims:

1-8. (canceled)

9. An exhaust purification system of an internal combustion engine,
comprising: an exhaust purification catalyst provided in an exhaust
passage of the internal combustion engine in a vehicle; a fuel supply
device which is provided in the exhaust passage upstream the exhaust
purification catalyst and supplies fuel to an exhaust gas flowing into
the exhaust purification catalyst; a heating device which heats the fuel
supplied from the fuel supply device; and a controller which controls the
heating device, wherein the controller controls the heating device to a
pre-heating temperature lower than an ignition threshold value capable of
igniting the fuel by supplying power to the heating device without
performing fuel supply by the fuel supply device when a first processing
request which stands if a state of the exhaust purification catalyst
requires combustion of the fuel is standing and a second processing
request which stands if an operating state of the vehicle allows exhaust
oxygen concentration suitable for combustion of the fuel to be supplied
is not standing, and controls the heating device to an ignition
temperature higher than the ignition threshold value when the first
processing request and the second processing request are standing and
controls the fuel supply device so that the fuel is supplied on condition
that the heating device has reached the ignition temperature.

10. The exhaust purification system of an internal combustion engine
according to claim 9, wherein the controller further controls the heating
device to the ignition temperature until the first processing request no
longer stands if the second processing request no longer stands after the
first and second processing requests stand.

11. The exhaust purification system of an internal combustion engine
according to claim 9, wherein the first processing request stands on
condition that a temperature of the exhaust purification catalyst is less
than a predetermined value.

12. The exhaust purification system of an internal combustion engine
according to claim 9, wherein the exhaust purification catalyst is an
occlusion-reduction type NOx catalyst, and the first processing request
stands on condition that a NOx occlusion amount of the exhaust
purification catalyst is larger than a predetermined value.

13. The exhaust purification system of an internal combustion engine
according to claim 9, wherein the exhaust purification catalyst is a
selective-reduction type NOx catalyst, and the first processing request
stands on condition that a reducing-agent occlusion amount of the exhaust
purification catalyst is smaller than a predetermined value.

14. The exhaust purification system of an internal combustion engine
according to claim 9, wherein the exhaust purification catalyst is an HC
adsorption catalyst, and the first processing request stands on condition
that an HC adsorption amount of the exhaust purification catalyst is
larger than a predetermined value.

15. The exhaust purification system of an internal combustion engine
according to claim 9, wherein the first processing request stands on
condition that a SOx accumulated amount of the exhaust purification
catalyst is larger than a predetermined value.

16. The exhaust purification system of an internal combustion engine
according to claim 9, wherein the second processing request stands on at
least either one of conditions that the vehicle is decelerating or the
internal combustion engine is idling.

Description:

TECHNICAL FIELD

[0001] The present invention relates to an exhaust gas purifying system
provided with a fuel supply device which supplies fuel to an exhaust
purifying catalyst provided in an exhaust passage of an internal
combustion engine.

BACKGROUND ART

[0002] A catalytic combustion device having the function of supplying fuel
to a catalyst arranged in the exhaust passage of the internal combustion
engine was proposed (See Patent Literature 1, for example). In this
device, fuel is supplied to the catalytic combustion section by a main
injector, while the fuel injected from a sub injector is ignited by a
spark plug, and the catalytic combustion section is pre-heated by the
flame.

[0003] In a device disclosed in Patent Literature 2, electricity is made
to flow between a central electrode and an outer-peripheral electrode
incorporated in the catalyst for purifying exhaust gas so as to pre-heat
the catalyst before the engine is started.

[0006] However, with the above-described device in Patent Literature 1,
deterioration of emission caused by a delay in the ignition of fuel
injected from the sub injector is not considered. Moreover, since the
device in the above-described Patent Literature 2 does not supply fuel to
the catalyst, deterioration of the emission caused by the fuel supplied
to the catalyst is not considered.

[0007] The present invention has the objective to provide new measure
capable of suppressing deterioration of the emission caused by an
ignition delay of fuel supplied to the catalyst.

Solution to the Problems

[0008] An aspect of the present invention is an exhaust purification
system of an internal combustion engine, comprising:

[0009] an exhaust purification catalyst provided in the exhaust passage of
the internal combustion engine in a vehicle;

[0010] a fuel supply device which is provided in the exhaust passage
upstream the exhaust purification catalyst and supplies fuel to the
exhaust gas flowing into the exhaust purification catalyst;

[0011] a heating device which heats the fuel supplied from the fuel supply
device; and

[0012] a controller which controls the heating device, wherein

[0013] the controller controls the heating device to a pre-heating
temperature lower than the ignition threshold value capable of igniting
the fuel if the first processing request based on the state of the
exhaust purification catalyst is standing and a second processing request
based on the operation state of the vehicle is not standing, and

[0014] controls the heating device to an ignition temperature higher than
the ignition threshold value if the first processing request and the
second processing request are standing.

[0015] In this aspect, the controller controls the heating device to the
pre-heating temperature lower than the ignition temperature if the first
processing request based on the state of the exhaust purification
catalyst is standing and the second processing request based on the
operation state of the vehicle is not standing. Moreover, the controller
controls the heating device to the ignition temperature if the first
processing request and the second processing request are standing.
Therefore, since the temperature of the heating device is raised to the
ignition temperature from a pre-heated state to the pre-heating
temperature, the ignition temperature can be quickly reached, and
deterioration of emission caused by the ignition delay of the fuel
supplied to the catalyst can be suppressed.

[0016] Preferably, the controller further controls the heating device to
the ignition temperature until the first processing request no longer
stands if the second processing request no longer stands after the first
and second processing requests stand. In this aspect, once the heating
device is controlled to the ignition temperature, the ignition lasts
until the first processing request no longer stands, and thus, the
processing of the catalyst requested by the first processing request can
be executed in a short time.

[0017] Preferably, the first processing request stands on condition that
the exhaust purification catalyst requires supply of fuel to the exhaust
passage and combustion of the supplied fuel. More preferably, the first
processing request stands on condition that the temperature of the
exhaust purification catalyst is less than a predetermined value.

[0018] If the exhaust purification catalyst is an occlusion-reduction type
NOx catalyst, the first processing request preferably stands on condition
that the NOx occlusion amount of the exhaust purification catalyst is
larger than the predetermined value.

[0019] If the exhaust purification catalyst is a selective reduction type
NOx catalyst, the first processing request preferably stands on condition
that the reducing agent occlusion amount of the exhaust purification
catalyst is smaller than the predetermined value. The selective reduction
type NOx catalyst includes those using urea aqueous as a reducing agent,
those using ammonium, and those using fuel (HC).

[0020] If the exhaust purification catalyst is an HC adsorption catalyst,
the first processing request preferably stands on condition that the HC
adsorption amount of the exhaust purification catalyst is larger than the
predetermined value.

[0021] Preferably, the first processing request stands on condition that
the SOx accumulated amount of the exhaust purification catalyst is larger
than the predetermined value.

[0022] Preferably, the second processing request stands on at least either
one of conditions that the vehicle is decelerating or the internal
combustion engine is idling.

[0023] Solutions to the problems in the present invention can be used in
combination as much as possible.

Advantages of the Invention

[0024] According to the present invention, deterioration of emission
caused by an ignition delay of the fuel supplied to the catalyst can be
suppressed.

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 is a conceptual diagram of an embodiment of the present
invention.

[0027] FIG. 3 is a time chart illustrating a car speed, a supply voltage
to the glow plug, and a glow-plug temperature in the embodiment.

BEST MOST FOR CARRYING OUT THE INVENTION

First Embodiment

[0028] A first embodiment of the present invention will be described
below. In FIG. 1, an exhaust purification system of an internal
combustion engine of the first embodiment has an engine main body 1, an
intake pipe 2, and an exhaust pipe 3. The engine main body 1 is a diesel
internal combustion engine but may be an internal combustion engine of
other types.

[0029] In the intake pipe 2, a throttle valve 4 and a surge tank 5 are
arranged. The throttle valve 4 is driven by a throttle actuator 7.
Injectors 6 for running are provided toward combustion chambers of the
engine main body 1.

[0030] The exhaust pipe 3 has the left side in FIG. 1 being the upstream
side and is connected to the engine main body 1 and the right side in the
figure being the downstream side and is connected to a muffler, not
shown. A catalyst 11 is provided in the exhaust pipe 3. The catalyst 11
is formed as an oxidation catalyst and can use Pt/CeO2,
Mn/CeO2, Fe/CeO2, Ni/CeO2, Cu/CeO2 and the like, for
example, as a catalytic substance. Cordierite or metal is used as a base
material of the catalyst 11.

[0031] In the exhaust pipe 3 upstream the catalyst 11, an injector 12 for
heating catalyst is installed with the injection port thereof faced
toward the inside of the exhaust pipe 3. Fuel in the fuel tank 13 is
supplied to the injector 12 through a pump 14. In order to promote
combustion, a pipeline, a control valve, and a compressor for supplying
air for combustion from the outside to the inside of the exhaust pipe 3
may be provided.

[0032] In the exhaust pipe 3 downstream the injector 12, a glow plug 15 is
provided. To the glow plug 15, a DC power source 16 for feeding power to
it and a drive circuit 17 are connected. The glow plug 15 is an
electrothermal heating device and capable of igniting fuel supplied from
the injector 12 by heating. As a heating device, a ceramic heater may be
used instead of the glow plug.

[0033] In the exhaust pipe 3 upstream the catalyst 11, an exhaust
temperature sensor 18 is installed. In the exhaust pipe 3 downstream the
catalyst 11, a NOx sensor 19 is installed. A water temperature sensor 23
is installed in a water jacket of the engine main body 1. In the
periphery of the throttle valve 2 in the intake pipe 2, an intake air
temperature sensor 24 is installed. Each of the sensors 18, 23, and 24
has a thermistor whose resistance value is changed in accordance with
temperature and it detects a temperature change by a resistance-value
change of the thermistor. The NOx sensor 19 includes a solid electrolyte,
for example. In the periphery of a driving wheel, not shown, a car speed
sensor 25 is installed to detect the car speed of a vehicle on which the
engine main body 1 is mounted is installed. In the intake pipe 2 in the
periphery of the throttle valve 4, an airflow meter 26 for detecting an
intake air amount.

[0034] An EGR (exhaust gas recirculation) passage 20 is provided
connecting the exhaust pipe 3 downstream the catalyst 11 and the intake
pipe 2 downstream the surge tank 5. In the EGR passage 20, an intercooler
21 for cooling the exhaust gas and an EGR control valve 22 for
controlling a flow rate are arranged.

[0035] Operations of the throttle actuator 7, the pump 14, the glow plug
15, the booster circuit 17, and the EGR control valve 22 are controlled
by an ECU (electronic control unit) 30.

[0036] The ECU 30 is a known one-chip microprocessor and includes a CPU, a
ROM, a RAM, a nonvolatile storage device, input/output interfaces, an A/D
converter, and a D/A converter. To the input interface of the ECU 30,
various sensors for detecting the state of the vehicle including the
engine operation state and the operation input state are electrically
connected, and a signal is inputted thereto. These various sensors
include a throttle opening sensor, a crank angle sensor, and an
accelerator pedal sensor in addition to the above-described exhaust
temperature sensor 18, the NOx sensor 19, the water temperature sensor
23, the intake air temperature sensor 24, the car speed sensor 25, and
the airflow meter 26.

[0037] To the output interface of the ECU 30, the injectors 6 and 12, the
pump 14, the drive circuit 17, and the EGR control valve 22 are
electrically connected, and a control signal is outputted therefrom. The
ECU 30 calculates a fuel supply instruction amount on the basis of
parameters indicating the state of the vehicle including the detected
value of each sensor and particularly the operation state of the engine
main body 1 and outputs a control signal so as to open the injectors 6
and 12 for a time in accordance with the instruction amount. Fuel in an
amount according to the fuel supply instruction amount is supplied from
the injectors 6 and 12 in accordance with this control signal.

[0038] The ROM of the ECU 30 stores various programs, maps and reference
values/initial values. The reference values stored in the ROM include a
pre-heating temperature T1 and an ignition temperature T2 which are
reference values of a glow-plug temperature used in processing described
later, and reference values used for determining whether or not a
catalyst request and a processing execution request are standing.

[0039] An operation of the first embodiment thus configured will be
described by referring to the flowchart in FIG. 2 and a time chart in
FIG. 3. In the first embodiment, the injector 12 and the glow plug 15 are
used for warming-up the catalyst 11. The flowchart in FIG. 2 is
repeatedly executed at every predetermined time during the operation of
the engine main body 1.

[0040] In FIG. 2, first, the ECU 30 reads a value of each parameter
relating to the state of the catalyst 11 and the operation state of the
vehicle (S10). The parameters read in here include an exhaust temperature
detected by the exhaust temperature sensor 18, a cooling water
temperature detected by the water temperature sensor 23, an intake air
temperature detected by the intake air temperature sensor 24, and an
operation state of the EGR control valve 22.

[0041] Subsequently, the ECU 30 determines whether or not the first
processing request based on the state of the catalyst 11 (hereinafter
referred to as a "catalyst request" as appropriate) is standing (S20). In
this embodiment, if an estimated catalyst temperature is lower than a
predetermined value, the catalyst request is standing. The estimated
catalyst temperature is calculated by the ECU 30 by using a predetermined
function or map on the basis of the exhaust temperature, cooling water
temperature, intake air temperature, and the operation state of the EGR
control valve, for example. The ECU 30 compares the calculated estimated
catalyst temperature with a predetermined reference value and if the
estimated catalyst temperature is lower than the reference value, the ECU
30 determines that the catalyst request is standing. If the catalyst
request is not standing, a negative answer is given at Step S20, and the
processing is returned.

[0042] If a positive answer is given at Step S20, that is, if the catalyst
request is standing, the ECU 30 performs a control output to the drive
circuit 17 so as to increase the voltage supplied to the glow plug 15
(S30). This voltage increase is repeatedly executed until the glow plug
15 reaches a pre-heating temperature T1 (S40). This pre-heating
temperature T1 is lower than the ignition threshold value Ti (See FIG. 3)
capable of igniting the fuel.

[0043] Subsequently, the ECU 30 determines whether or not a second
processing request based on the operation state of the vehicle
(hereinafter referred to as a "processing execution request" as
appropriate) is standing (S50). In this embodiment, the processing
execution request is standing if the car speed detected by the car speed
sensor 25 is decelerating. If the car speed is not decelerating, the
processing execution request does not stand, and a negative answer is
given at Step S50, and the processing is returned.

[0044] If a positive answer is given at Step S50, that is, if the
processing execution request is standing, the ECU 30 performs a control
output to the drive circuit 17 and further increases the voltage supplied
to the glow plug 15 (S60). This voltage increase is repeatedly executed
until the glow plug 15 reaches the ignition temperature T2 (S70). This
ignition temperature T2 is higher than the ignition threshold value Ti
capable of igniting the fuel.

[0045] On condition that the distal end portion of the glow plug 15
reaches the ignition temperature T2, the ECU 30 controls the injector 12
so as to inject the fuel into the exhaust pipe 3 (S80). The fuel injected
from the injector 12 is ignited by the glow plug 15 and combusted. Flame
F generated by this combustion heats the catalyst 11. Since it is
guaranteed that the glow plug 15 has reached the ignition temperature T2
at the time when the fuel is injected (S70), misfiring of the fuel is
suppressed.

[0046] Subsequently, the ECU 30 determines again whether or not the first
processing request (that is, the catalyst request) is standing (S90).
Until the catalyst request is no longer standing, the processing from
Step S60 to Step S80 is repeatedly executed. Therefore, even if the
processing execution request is no longer standing after the catalyst
request and the processing execution request were standing (S20, S50),
the glow plug 15 is continuously controlled at the ignition temperature
T2 until the catalyst request is no longer staindig. If the catalyst
request is no longer standing, that is, if the catalyst temperature
becomes higher than a predetermined value, a negative answer is given at
Step S90 and the processing is returned.

[0047] Changes in the car speed, the glow plug supply voltage and the
glow-plug temperature when the above-described series of processing is
executed will be described in accordance with the time chart in FIG. 3.
When the car speed rises from the idling state (t0) and the catalyst
request based on the state of the catalyst 11 is standing (S20) during
running at a constant speed, the glow plug 15 is controlled to the
pre-heating temperature T1 lower than the ignition temperature T2 (S30,
S40, t2) until the processing execution request based on the operation
state of the vehicle (S50) stands. Then, if deceleration of the vehicle
is detected (t3), the catalyst request and the processing execution
request stand (positive at S50), and thus, the glow plug 15 is controlled
to the ignition temperature T2 (t3). Even if the deceleration is finished
(t4) and the processing execution request no longer stands, the
temperature of the glow plug 15 is continuously executed until the
catalyst request no longer stands (t5).

[0048] If pre-heating from Step S20 to Step S40 is not performed, in
response to the detection of deceleration of the vehicle (t3), the power
feed to the glow plug 15 is started (two-dot chain line a), but due to a
delay in temperature rise of the glow plug 15, the temperature of the
glow plug 15 does not reach the ignition threshold value Ti by the end of
the deceleration (t4) (two-dot chain line b) or even if reached,
deterioration of emission cannot be suppressed due to the delay in
ignition. On the contrary, in this embodiment, since the pre-heating is
performed, the ignition temperature T2 can be quickly reached.

[0049] As thus described in detail, in this embodiment, the ECU 30
controls the glow plug 15 to the pre-heating temperature T1 lower than
the ignition temperature T2 (S30, S40) when the catalyst request based on
the state of the catalyst 11 is standing (S20) and the processing
execution request based on the operation state of the vehicle (S50) is
not standing. When the catalyst request and the processing execution
request are both standing, the glow plug is controlled to the ignition
temperature T2. Therefore, since the temperature of the glow plug 15 is
raised to the ignition temperature T2 from the pre-heated state to the
pre-heating temperature T1, the ignition temperature T2 can be quickly
reached, and deterioration of emission caused by a delay in ignition of
the fuel supplied to the catalyst 11 can be suppressed. Moreover, if the
glow plug 15 is pre-heated all the time, energy loss during standby time
would be large, but since the pre-heating is started at the time when the
catalyst request stands in this embodiment, energy consumption required
for pre-heating can be suppressed.

[0050] Moreover, in this embodiment, after the catalyst request and the
processing execution request were standing (S20, S50), even if the
processing execution request no longer stands, the ECU 30 controls the
glow plug 15 to the ignition temperature T2 until the catalyst request no
longer stands (S90). Therefore, once the glow plug 15 is controlled to
the ignition temperature T2, the ignition is continued (S90) until the
catalyst request no longer stands, and thus, processing of the catalyst
11 requested by the catalyst request can be executed in a short time.

[0051] In order to favorably combust the fuel supplied from the injector
15, the fuel supply and ignition are preferably performed in the
operating state in which oxygen concentration in the exhaust gas is high
(during deceleration of the vehicle or idling of the engine main body 1,
for example). Thus, the second processing request (processing execution
request) may be set to stand on at least either one of the conditions of
deceleration of the vehicle and idling of the engine main body 1.

Second Embodiment

[0052] Subsequently, a second embodiment of the present invention will be
described. The second embodiment is configured such that an
occlusion-reduction type NOx catalyst (NSR: NOx Storage Reduction) is
used as the catalyst 11. In this case, the catalyst 11 is formed by
carrying precious metal such as platinum Pt as a catalyst component and a
NOx absorption component on the surface of a base material formed of an
oxide such as alumina Al2O3 or the like. The NOx absorption
component is made of at least one selected alkali metal such as kalium K,
sodium Na, lithium Li, cesium Cs and the like; alkali earth such as
barium Ba, calcium Ca and the like; and rare earth such as lanthanum La,
yttrium Y and the like.

[0053] The catalyst 11 which is an occlusion-reduction type NOx catalyst
performs NOx absorption/emission action in which it absorbs NOx (nitrogen
oxide) when the air-fuel ratio of the exhaust gas flowing therein to is
leaner than a predetermined value (typically, a theoretical air-fuel
ratio), while it emits the absorbed NOx if the oxygen concentration in
the exhaust gas flowing therein to becomes lower. Since a diesel engine
is used in this embodiment, the exhaust air/fuel ratio is lean in a
normal time and the catalyst 11 absorbs NOx in the exhaust gas. Moreover,
if the fuel as a reducing agent is supplied on the upstream side of the
catalyst 11 and the air/fuel ratio of the inflow exhaust gas becomes
rich, the catalyst 11 emits the absorbed NOx. Then, this emitted NOx
reacts with the reducing agent and is reduction-purified.

[0054] In the second embodiment, the first processing request (catalyst
request) stands on condition that the NOx occlusion amount of the
catalyst 11 is larger than the predetermined value. The NOx occlusion
amount can be estimated by a predetermined function or map using an
integrated value from execution of the previous reduction processing of
the exhausted NOx amount obtained from a fuel injection mount from the
injector 6 and an engine rotation number Ne.

[0055] The higher the engine rotation number Ne becomes or the larger the
fuel injection amount becomes, the more the NOx exhaust amount increases.
The ECU 30 obtains the NOx exhaust amount corresponding to an actual
engine operating state, that is, the engine rotation speed NE and the
fuel injection amount and integrates the amount momentarily. An
accelerator opening degree or a throttle opening degree can be used
instead of the fuel injection amount, for example.

[0056] In the second embodiment, if the NOx occlusion amount which is an
integrated amount of this NOx exhaust amount exceeds a predetermined
reference NOx occlusion amount, it is determined that the catalyst
request is standing, while if the NOx occlusion amount does not exceed
the reference NOx occlusion amount, it is determined that the catalyst
request is not standing. The reference NOx occlusion amount may be a
constant value or dynamically obtained as a function of the temperature
of the catalyst 11. The remaining processing and mechanical configuration
of the second embodiment are the same as those in the first embodiment.

[0057] In the second embodiment thus configured, and in the third to
seventh embodiments described below, since the temperature of the glow
plug 15 is raised from the pre-heated state to the pre-heating
temperature T1 to the ignition temperature T2 similarly to the first
embodiment, the ignition temperature T2 can be quickly reached, and
deterioration of emission caused by the ignition delay of the fuel
supplied to the catalyst 11 can be suppressed. Moreover, once the glow
plug 15 is controlled to the ignition temperature T2, the ignition is
continued until the catalyst request does no longer stand (S90), and
thus, the processing of the catalyst 11 requested by the catalyst request
can be executed in a short time.

Third Embodiment

[0058] Subsequently, a third embodiment of the present invention will be
described. The third embodiment is configured with the catalyst 11 as an
occlusion-reduction type NOx catalyst similarly to that in the second
embodiment, and the first processing request is obtained on the basis of
the NOx purification amount.

[0059] The NOx purification amount is a value indicating NOx purification
capability of the catalyst 11 and is obtained by subtracting the NOx
amount on the downstream of the catalyst from an estimated NOx exhaust
amount from the engine main body 1. The estimated NOx exhaust amount is
estimated on the basis of the engine's operating state, that is, the
engine rotation speed NE and the fuel injection amount (the accelerator
opening degree or the throttle opening degree may be used instead). The
NOx amount on the downstream of the catalyst is detected by the NOx
sensor 19. The NOx purification capability of the catalyst 11 differs
depending on the catalyst bed temperature. Thus, the ECU 30 determines
whether or not the first processing request (catalyst request) is
standing on the basis of the NOx purification amount and the current
catalyst bed temperature. That is, the ECU 30 determines that the
catalyst request is standing if the NOx purification amount is larger
than a reference value according to the current catalyst bed temperature
and determines that the catalyst request is not standing if the NOx
purification amount is smaller than the reference value according to the
current catalyst bed temperature on the contrary. The remaining
processing and mechanical configuration of the third embodiment are the
same as those in the above-described first embodiment.

[0060] The first processing request may be obtained by another parameter
relating to deterioration of the purification capability of the catalyst
11. For example, since the larger the deterioration degree of the
catalyst is, the lower the reaction heat in the catalyst becomes, it may
be determined whether the catalyst request is standing or not on the
basis of the estimated catalyst bed temperature calculated from the
exhaust temperature, the fuel supply amount from the injector 12, and the
air-fuel ratio of the engine main body 1 and the current catalyst bed
temperature detected by a temperature sensor (not shown) provided in the
catalyst 11. In this case, the ECU 30 can determine that the catalyst
request is standing if the difference between the former and the latter
is large (or a ratio of the latter to the former is small), or on the
contrary, the ECU 30 can determine that the catalyst request is not
standing if the difference between the former and the latter is small (or
the ratio of the latter to the former is large).

Fourth Embodiment

[0061] Subsequently, a fourth embodiment of the present invention will be
described. The fourth embodiment is configured with the catalyst 11 as a
urea selective-reduction type NOx catalyst (SCR: Selective Catalytic
Reduction). In this case, the catalyst 11 can be configured as those
carrying precious metal such as Pt on the surface of a base material such
as zeolite, alumina or the like, those carrying transition metal such as
Cu subjected to ion exchange on the base material surface, or those
carrying titania/vanadium catalyst (V2O5/WO3/TiO2) on
the base material surface, for example.

[0062] In this urea selective-reduction type NOx catalyst, a urea aqueous
solution is used as a reducing agent, and an apparatus is provided with
an injecting device for supplying the reducing agent immediately before
the catalyst 11. The supplied urea aqueous solution changes to ammonia
(NH3) in the exhaust gas and is occluded in the catalyst 11. Under a
condition that the air-fuel ratio of the inflow exhaust gas is lean, HC
and NO in the exhaust gas react with ammonia occluded into the catalyst
11 steadily and simultaneously and purified to N2, CO2, and
H2O. Ammonium may be also used as a reducing agent.

[0063] In the fourth embodiment, the first processing request (catalyst
request) stands on condition that the ammonium occlusion amount of the
catalyst 11 is smaller than a predetermined value. The ammonium occlusion
amount can be calculated by subtracting the ammonium consumption amount
from the ammonium supply amount to the catalyst 11, for example. The
ammonium supply amount can be obtained by a predetermined function or map
on the basis of the integrated amount of the supplied urea aqueous
solution and the estimated catalyst temperature (this can be calculated
on the basis of an engine cooling water temperature or the like). The
ammonium consumption amount can be obtained by a predetermined function
or map on the basis of the estimated NOx exhaust amount (this can be
calculated on the basis of a fuel injection amount from an in-cylinder
fuel injection valve) and the estimated catalyst temperature. The
remaining processing and mechanical configuration of the fourth
embodiment are the same as those in the above-described first embodiment.

Fifth Embodiment

[0064] Subsequently, a fifth embodiment of the present invention will be
described. The fifth embodiment is configured with the catalyst 11 as an
HC selective-reduction type NOx catalyst (HC-SCR). In this case, the
catalyst 11 can be configured by those carrying silver-added alumina
(Ag/Al2O3) on a ceramic honeycomb, or using zeolite, for
example. The catalyst 11 selectively reduces NOx to N2 in a
temperature region from approximately 250 to 600° C., for example,
by using light oil (hydrocarbon, HC) as a reducing agent.

[0065] In the fifth embodiment, the first processing request (catalyst
request) stands on condition that the HC occlusion amount of the catalyst
11 is smaller than a predetermined value. The HC occlusion amount can be
calculated by subtracting the HC consumption amount from the HC supply
amount to the catalyst 11, for example. The HC supply amount can be
obtained by a predetermined function or map on the basis of the
integrated fuel injection amount from the injectors 6 and 12 and the
estimated catalyst temperature (this can be calculated on the basis of
the engine cooling water temperature and the like). The HC consumption
amount can be obtained by a predetermined function or map on the basis of
the estimated NOx exhaust amount (this can be calculated on the basis of
the fuel injection amount from the in-cylinder fuel injection valve) and
the estimated catalyst temperature. The remaining processing and
mechanical configuration of the fifth embodiment are the same as those in
the above-described first embodiment.

Sixth Embodiment

[0066] Subsequently, a sixth embodiment of the present invention will be
described. The sixth embodiment is configured with the catalyst 11 as an
HC adsorption catalyst. In this case, the catalyst 11 is made of zeolite
(FER, MOR, FAU, MFI, β-zeolite and the like), for example, and
adsorbs and holds HC at a low temperature while the catalyst 11 emits and
oxidizes the adsorbed/held HC at a high temperature.

[0067] In the sixth embodiment, the first processing request (catalyst
request) stands on condition that the HC adsorption is larger than a
predetermined value. The HC adsorption amount can be calculated by
subtracting the HC consumption amount from the HC supply amount to the
catalyst 11, for example. The HC supply amount can be obtained by a
predetermined function or map on the basis of the integrated fuel
injection amount from the injectors 6 and 12 and the estimated catalyst
temperature (this can be calculated on the basis of the engine cooling
water temperature and the like). The HC consumption amount can be
obtained by a predetermined function or map on the basis of time when a
predetermined oxidation threshold value of the estimated catalyst
temperature is exceeded and the HC adsorption amount at that time. The
remaining processing and mechanical configuration of the sixth embodiment
are the same as those in the above-described first embodiment.

Seventh Embodiment

[0068] Subsequently, a seventh embodiment of the present invention will be
described. The seventh embodiment is configured with the catalyst 11 as
the occlusion-reduction type NOx catalyst similar to the above-described
second embodiment, and the first processing request is obtained on the
basis of a SOx (sulfur oxide) accumulated amount of the catalyst 11.

[0069] SOx is considered to be generated by the bond between a sulfur
component S in the fuel and oxygen O2 in intake air through
combustion, which is accumulated on a catalyst as a sulfate X--SO4
(Al2 (SO4)3, Ce2 (SO4)3, for example). The
SOx accumulated amount is calculated as an integrated value after the
previous processing of sulfur concentration in the fuel and the fuel
consumption amount in the engine main body 1.

[0070] The ECU 30 determines that the catalyst request stands if the SOx
accumulated amount is larger than a reference value while the ECU 30
determines that the catalyst request does not stand if the SOx
accumulated amount is smaller than the reference value. The remaining
processing and mechanical configuration of the seventh embodiment are the
same as those in the above-described first embodiment.

[0071] The present invention has been described with some degree of
specificity, but it should be understood that various alterations and
changes can be made without departing from the spirit and scope of the
claimed invention. Various technical measures illustrated in each of the
above-described embodiments and each variation can be combined with each
other as much as possible. In each of the above-described embodiments and
each variation, the first and second processing requests were supposed to
be composed of a single type, respectively, but each may be a combination
of a plurality of types of processing requests.